Chemical straightening and the scalp: what studies report

Rebonding, relaxing, keratin smoothing and other chemical straightening treatments are a common part of salon life in Malaysia. Many people use them for years without major problems. Others notice burning, flaking, breakage or thinning afterwards and wonder whether the treatment is to blame. Here is a calm look at what the research says.

What chemical straightening does

Straightening products work by changing the internal bonds that give hair its natural shape. To do that, they must act on the hair fibre itself, which is why they can also weaken it. A review of hair cosmetics notes that shampoos, hair dyes and straightening products may alter hair fibre structure, remove lipids and cause protein loss ¹.

What the studies report

A 2022 review in a Brazilian dermatology journal looked at 33 articles published between 2000 and 2020 on chemical straighteners ². It found:

• Scalp effects: in some studies, hair relaxers were associated with eczema, flaking (desquamation), pain, burns and inflammation of the scalp ².
• Hair effects: hair loss, damage to the hair shaft, changes in hair colour and changes in the amino acid make-up of the hair were observed ².
• Mixed results: the findings varied across studies, and the long-term effects are still unknown ².

The same review notes that straightening became popular in Brazil with formaldehyde and related chemicals, even though current law there prohibits this use ². This is a reminder that what is actually in a salon product is not always clear to the customer.

A separate study from India compared 94 women. Those who had blow-drying, straightening, flat ironing or perming in the previous six months were far more likely to show microscopic damage to their hair than women who had not, although hair density and breakage scores were similar between the groups ³. In other words, damage can be present at a level you cannot see before it shows up as breakage.

Breakage or true hair loss?

It helps to separate two problems:

• Breakage happens along the hair shaft. You see short, snapped pieces, rough ends and frizz, but the roots are still growing. A review lists hair breakage, frizz and contact dermatitis among possible side effects when hair cosmetics are misused ¹.
• Hair loss from the root means fewer hairs growing. Scalp burns and inflammation from harsh chemicals are a concern because they affect the skin where hair grows ².

If you are not sure which you have, see fine hair or thinning hair.

Tension adds to the risk

Straightened hair is often worn sleek and pulled back. The American Academy of Dermatology (AAD) warns that tight buns, ponytails and updos, and hair extensions or weaves, especially on relaxed hair, can lead to traction alopecia, a type of hair loss caused by constant pulling ⁴. The hairline is often one of the first places it shows ⁴.

How to lower the risk

• Space out treatments. Fewer chemical processes means less repeated stress on the hair and scalp.
• Do not combine harsh processes on the same day, such as straightening and bleaching.
• Ask what is in the product. Be cautious of strong fumes or eye irritation during a treatment, and stop if your scalp burns.
• Never apply to an irritated or broken scalp. Wait until any sores, sunburn or flaking have settled.
• Limit heat afterwards. The AAD advises limiting blow-drying and flat or curling irons, using low or medium heat and a heat-protecting product ⁵.
• Be gentle when wet. Use a wide-tooth comb and blot hair with a towel instead of rubbing ⁵.
• Avoid tight styles on chemically treated hair ⁴.

For a full routine, see a gentle hair care routine. For styling ideas when hair is thin, see making thin hair look fuller.

If you are already treating hair loss

The hair cosmetics review points out that hair care habits matter for people with alopecia. Poor product choices or rough grooming can make people give up on prescribed treatments such as topical minoxidil, while using products properly may help people stay with treatment ¹. It also notes that dyeing and straightening raise particular concerns for pregnant women and people with sensitive hair and scalp ¹.

If you use a scalp treatment, ask your doctor or pharmacist how to time it around salon visits.

When to see a doctor

See a doctor or dermatologist if:

• your scalp blisters, weeps, or stays painful or red after a treatment
• you notice patches of hair loss, or the hairline is receding
• thinning continues for months after you stop chemical treatments

Some scalp conditions that cause scarring need early care. See hair loss red flags and when to see a dermatologist. For general first steps, see what to do when you first notice hair loss.

Frequently asked questions

Can rebonding or relaxing cause hair loss?

A review of 33 articles found hair loss, shaft damage and scalp inflammation reported with straighteners, though findings varied ².

Is the damage always visible?

Not always. One study found more microscopic hair changes in women who had straightening or heat styling, even though density was similar ³.

Are tight styles a problem on relaxed hair?

Yes. The AAD warns that extensions or weaves, especially on relaxed hair, and tight styles can cause traction alopecia ⁴.

Are the long-term effects known?

No. The review states the long-term effects of chemical straighteners remain unknown ².

Educational content. Not medical advice.